One efficiency measure in diode laser packages is the ratio of the amount of optical power emitted from one or more diode lasers and the amount of useful optical power that is output from the package. This optical to optical efficiency, even when maximized through optical design, is impaired by losses resulting in the formation of stray light inside the laser package. The loss typically ranges from a few percent to many tens of percent, depending on the complexity of the structure and optical coupling of a particular device. Laser diode package housings are often made of a thermally conductive material, such as copper or aluminum, which can serve to couple heat out of the package for convective or further conductive cooling. Complex water-based cooling systems can be integrated with one or more diode laser packages to provide package cooling, and are particularly relied upon to increase package lifetime as diode power or diode package power density increases.
In the art of laser packaging, mechanical structures and features are often highly reflective, for example, by being gold-plated or soldered. In virtually all packages, it has been found herein that stray laser light reflects off these internal package surfaces or structures, until it is finally absorbed into a surface. Features that are not highly reflective, and thus absorbing a proportionally larger percentage of light, include epoxies, diode laser thermal substrates, electrical insulating coatings, etc., each of which are often not intended or designed to be robust to laser light. Lower power packages in the industry are usually able to dissipate this heat as it is relatively low magnitude, without significant impact to epoxies, lasers or other structures, and so reflected light has been ignored. In higher power packages, such as packages generating 10 W to 300 W or more of laser energy, this results in 1 W to 300 W, or more, of stray light and therefore heat, which the inventors have found causes degradation of optical surfaces, such as coatings, and other internal components, such as epoxies. This stray light may also be absorbed into the laser diode or laser diode substrate, resulting in diode wavelength change, reduced diode lifetime, or laser instability. Heating of opto-mechanical structures within the package, including solder, epoxy, etc., can cause in optical misalignment, PIF (package induced failure) through outgassing, and result in premature laser, thermal, structural, or optical failure. Conventional packages typically address increased heat load with active cooling systems alone, which increases cost significantly. Accordingly, there remains a need for improvements to diode laser package heat management with fewer drawbacks.